A device to track and record the motion of the left ventricular (LV) border in the intact animal has been designed. The system involves the use of radar type, "track-while-scan-techniques" applied to video signals of the heart from a portable fluoroscope image intensifier. The tracking wave index in several animal experiments correlated significantly with the first derivative of LV pressure, LV strain gauge displacement and peak flow velocity, when the contractile state of the heart was altered by pharmacologic agents. A series of patients following open heart surgery will undergo contractility studies in the postoperative period by standard hemodynamic methods in present use. These studies will be simultaneously compared to data obtained by heart tracking. It is hoped that Heart-Tracking will provide simple, non- invasive method of quantitating alterations of myocardial contractility in man.